Project Summary/Abstract We will attempt to recapitulate mitochondrial evolution based on the endosymbiotic theory. Eukaryotic organelles, like mitochondria and chloroplasts, are proposed to have evolved from bacterial endosymbionts during an early stage of evolution. Here we will begin to test this theory using two well established model organisms ? E. coli and S. cerevisiae. Specifically, we will generate bacterial endosymbionts in yeast cells. Once we establish stable endosymbionts we will systematically either knockout large parts of the bacterial genome or move specific genes to the host genome to obtain a minimal symbiont genome similar to the early stages of mitochondrial evolution. We will also attempt to further delete genes in the yeast mitochondria, explore those factors that affect the stability of this system and light utilizing endosymbionts using yeast and cyanobacteria. These studies have the potential to provide additional insights into the evolution of complex eukaryotic functions, such as energy generating mitochondria.